In the field of data communications, a modem is used to convey information from one location to another. Digital Subscriber Line (DSL) technology now enables modems, or DSL devices, to communicate large amounts of data. Typically in a communications environment a single copper wire pair is used to convey both digital data and analog voice information, such as in the case of a digital subscriber line providing both digital data service and conventional voice service, to a residential or a business location.
The DSL device is typically connected to the local loop (the copper wire provided by the local telephone company serving the remote location), or communications channel, through a conventional hybrid transformer. In this arrangement, a splitter, typically known in the field of telephony communications as a Plain Old Telephone Service (POTS) splitter, is installed at the remote location to allow the connection of a conventional telephone to the communication line. A POTS splitter may also be installed at a central office location. A POTS splitter isolates the communication line from most low frequency harmonic distortion components introduced by, for example, a conventional telephone connected to the communication line. A POTS splitter, however, adds cost and complexity and is typically failure prone. Eliminating the POTS splitter, however, may permit audible harmonic distortion, caused by, for example, a conventional telephone connected to the line, to enter the communication path, thus degrading the digital data service and causing audible interference to the voice service. Heretofore, there has been no way to cancel the audible harmonic distortion without the use of a device such as a POTS splitter.
Thus, it is desirable to adaptively cancel, within a DSL device, the non-linear out of band audible harmonic distortion caused by a conventional telephone, or other device, connected to a remote communication line.